Earth's Place in the Universe

According to the CSET test guide, there will be a total of 50 multiple choice questions and three constructed response questions for CSET 122.

a. Identify and describe characteristics of galaxiesGalaxy: a great island of stars in space, all held together by gravity and orbiting a common center

There are three major types of galaxies:

Elliptical

Spiral

Irregular

Elliptical Galaxies

These types of galaxies have very little cool gas and dust. There are few young stars and consists primarily of old red stars. These galaxies vary widely in size. Large galaxies can reach 300 million light years in diameter. Dwarf ellipticals (which are very common) may contain 1/100,000th as many stars as the Milky Way. Contains very hot ionized gas. One example of an elliptical galaxy is the M87.

Spiral Galaxies

Spiral galaxies can extend to a radius of more than 100,000 light years. These types of galaxies consists of a disk component and a spheroidal component.

Disk component: this is the flat disk in which stars follow an orderly, circular path around the galactic center. There is always an interstellar medium of gas and dust. Contains stars of all ages and masses.

Spheroidal component: The bulge and halo makes up the spheroidal component. Stars in this region have orbits with many different inclinations. There is little cool dust and gas. Stars here are generally old and low in mass.

All spiral galaxies contains these two components, but there are variations. There are two variations of spiral galaxies:

Barred Spiral galaxies: These galaxies appear to have a straight bar of stars cutting across the center, which spiral arms curling away from the ends of the bar. Approximately 2/3 of all spiral galaxies are barred and it is suspected based on evidence from the Sptizer Space Telescope that our Milky Way Galaxy may be a barred spiral galaxy. Bars are thought to be temporary phenomena in the life of a spiral galaxy. Eventually, the bar decays over time and the barred spiral galaxy becomes a regular spiral galaxy. Example: M58

Lenticular galaxies: These galaxies tends to have less cool gas than normal spirals, but has more than elliptical (thus this types of galaxy is sometimes referred as an intermediate class between spirals and ellipticals). They contain mainly aging stars. They lack, or have poorly defined spiral arms. Example: IC 1101

Irregular Galaxies

These are blobby star systems that do not have a distinct shape like the elliptical or spiral galaxies have. These galaxies do not all into one of the regular classes of the Hubble Sequence. They are often chaotic in appearance. It is thought that they make up a quarter of all galaxies. Most irregular galaxies were once spiral or elliptical but were deformed by disorders in gravitational pull. They are usually white and dusty and contains young, massive stars. Telescopic observations probing deep into the universe shows us that distinct galaxies are more likely to be irregular in shape.

There are three types of irregular galaxies:

Irr I: These galaxies have some structures, but not enough to place it on the Hubble Sequence.

Irr II: these galaxies have absolutely no structures to place it on the Hubble Sequence.

DI: these are dwarf irregular galaxies. These galaxies have low levels of metallicities and high levels of gas. These types of galaxies are thought to be important because they are thought to be similar to the earliest types of galaxies.

b. Explain the evidence for the “big bang” model

The "Big Bang" model has gained wide scientific acceptance for two key reasons:

1) Radiation: radiation that began to stream across the universe at the end of the era of nuclei should still be present today. Scientists find that the universe if filled with cosmic microwave background. Arno Penzias and Robert Wilson were physicists who found unexpected noise of the wave antennae designed for satellite communication. The cosmic microwave background consists of photons arriving at Earth directly from the end of the era of the nuclei when the universe was about 380,000 years old. Because natural atoms finally could remain stable, they captured most of the electrons in the universe with no more free electrons to block them, the photons from the epoch have flown unobstructed through the universe ever since. When we observe the cosmic microwave background, we are essentially seeing back to a time when the universe was only 380,000 years old. The spectrum of the cosmic wave background originally peaked in visible light (when the temperature of the universe was around 3,000 K). The universe has expanded by a factor of around 1000, thus stretching the wavelengths of the photons by the same amount. Thus, their wavelengths have shifted about a millimeter, into the microwave portion of the spectrum and corresponding to a temperature of a few degrees above zero.

In the 1990s, NASA satellite COBE (Cosmic Background Explorer) was launched to test these ideas about the cosmic microwave background. What it found was that the microwave background does have a perfect thermal radiation spectrum, with a peak corresponding to a temperature of 2.73 K. The temperature of the night sky is a frigid 3 degrees above absolute zero. COBE also mapped the temperature of the cosmic microwave background in all directions. COBE showed that the cosmic microwave background is no quite perfectly uniform (due to regions of enhanced density). COBE shows that temperature varies slightly from one place to another by a few parts in 100,000. WMAP (Wilkinson Microwave Aniostropy Probe) also has proven the confirmation of small temperature variations. These temperature variations indicate that the density of the early universe really did differ slightly from place to place.

2) Abundances of elements: The Big Bang predicts that some of the original hydrogen in the universe should have fused into helium during the era of nucleosytnthesis. Observation of the actual helium content of the universe closely matches the amount of the helium predicted by the big bang model. No galaxy has a helium fraction lower than 25%. The majority of helium in the universe must have already been present in the protogalactic clouds that preceded the formation of galaxies. Thus, the universe must have been hot enough to fuse hydrogen into helium. During the era of nucleosynthesis, the universe was hot enough for protons to convert into neutrons and vice versa. But, as the universe cooled, the neutron-proton conversion reaction began to favor protons. Neutrons are slightly more massive than protons so the reactions that converted protons to neutrons require more energy to proceed. By the time the temperature dropped to 1010 K, protons began to outnumber neutrons. The universe was till hot enough for fusion to take pace. Protons and neutrons combined to form deutrium and deutrium nuclei fused to form helium. However, the helium nuclei was being blasted apart by the gamma rays that filled the universe. Calculations show that there was a 7 to 1 proton-neutron ratio. Thus, the universe should have had a composition of 75% hydrogen and 25% helium by mass at the end of the nucleosynthesis era. So, the Big Bang gave rise only to two elements, hydrogen and helium. Heavier elements were produced later by massive stars through nuclear fusion in their cores or in the expulsion that accompany their deaths and release much of their content into space.

The Big Bang didn't produce heavier elements because by the time stable helium nuclei formed (within the big bangs first minute of life), the temperature and density of the rapidly expanding universe had dropped too far for the process of heavier elements to be formed (such as carbon which requires three helium nuclei to fuse).

c. Know that the sun is a typical star and is powered by nuclear reactions, primarily the fusion of hydrogen to form helium

Nuclear fusion requires extremely high temperature and density. These conditions are found deep in the core. In order for the sun to shine steadily, it must have a way to keep the core hot and dense. It maintains these internal conditions through a natural balance between two competing forces: gravity pulling inward and pressure pushing outward. This balance is called a gravitational equilibrium. The outward push against gravity comes form internal gas pressure. The weight of overlying layers is greater as we look deeper into the sun, the pressure must increase with depth. In the core, the pressure makes the gas hot and dense enough to sustain nuclear fusion. The energy released by fusion, in turn, heats the gas and maintains the pressure that keeps the sun in balance against the inward upll of gravity. The sun began to fuse 4.5 billion years ago when gravitational contraction made the sun hot enough to sustain nuclear fusion in tits core. A collapsing cloud of intersletter gas in contracted by gravity and becomes hot enough to sustain nuclear fusion.

The sun is a ball of hot gas (actually, a ball of plasma, which just means that it is a gas in which the atoms are ionized due to high temperature. Within the core, it reaches 15 million Kelvin. Thus, the plasma is like a soup of hot gas with positively charge atomic nuclei and charged electrons whizzing about at very high speeds. At any one time, these nuclei are on a high speed collision course with each other. In most cases, the electromagnetic forces deflect the nuclei, preventing collisions. If the nuclei do collide with sufficient energy, then they can for ma heavier nucleus. The strong force is the only force in nature that can overcome electromagnetic repulsion and bind protons and neutrons together. Gravitational and electromagnetic forces drop off gradually as distance between particles increases. The strong force overpowers electromagnetic force over small distance but is insignificant when distance between particles exceed the typical sizes of atomic nuclei. The high pressure and temperature within the solar core are just right for fusion of hydrogen nuclei into helium nuclei. The high temperature is important because nuclei must collide at very high speeds in order to overcome the electromagnetic repulsion and come close enough to fuse. The higher the temperature, the harder the collision.

The sequence of steps that occurs in the sun is called the proton-proton chain because it begins with the collisions between individual protons. 4 protons combine to make 1 helium nucleus. 2 protons fuse to make deuterium (1 proton and 1 neutron). The step occurs twice. The deuterium nucleus and a proton fuse to make a nucleus of helium -3 (2 proton and 1 neutron). This step occurs twice. Two helium-3 nucleus fuse to form helium 4(2 proton and 2 neutron_) releasing two excess protons in the process. Fusion of hydrogen in helium generates energy because a helium nucleus has a mass slightly less than the combined mass of 4 hydrogen nuclei. So, when 4 Hydrogen nuclei fuse into a helium nucleus, a little bit of mass disappears. The disappearing mass becomes energy in accord to E=mc2.

d. Describe the process of the nuclear synthesis of chemical elements and how accelerators stimulate the conditions for nuclear synthesis

Originally, the “big bang” is thought to have produced helium, hydrogen, and trace amounts of lithium. Heavier elements were produced later on by massive stars through nuclear fusion in their cores. However, nuclear fusion in stars only produces elements in the periodic table up to iron. A low-mass star can only produce elements up to carbon. This is because the degeneracy pressure halts the contraction of its inert carbon core before it can get hot enough for fusion (carbon fusion is possible only at temperatures above 600 million K). A high-mass star, however, has no problems and is able to keep its carbon core hot enough so that degeneracy pressure doesn't come into play. So, after the fusion of helium stops, the gravitational contraction in the carbon core continues until it reaches 600 million K that is required to fuse carbon into heavier elements. Then, when the carbon runs out, the core begins to collapse again. As it collapses, the star shrinks and heats up, producing the heavier elements, up to iron. Elements heavier than iron are produced in cataclysmic explosions known as supernovae. Heavier element content of the galaxy rose with each generation of massive stars.

Scientists have created accelerators to mimic the fusion reaction that takes place within a star's core. These particle accelerators were built so that the velocity of the particles was high enough to overcome the electrostatic repulsion that normally repels particles from each other. Once energy is high enough to overcome this repulsion, then fusion can take place. The first accelerator was built in the 1950s in Berkley and scientists continue to explore fusion as a possible potential source of energy.

e. Compare the use of visual, radio, and x-ray telescopes to collect data that reveal that stars differ in life cycles

If a group of aliens quickly flew by earth and took a snapshot of the people on earth, they can tell that there are different kinds of people. There are old people, young people, babies, teens, some are big, some are small, different color skin, etc. So, by using different tools, we can tell that stars also differ. They differ in color, size, surface gravity, and in temperature. However, it is impossible to actually watch a star grow from birth. So, just like looking at a snapshot of humans, we use information by studying different stars to help us to put together an average life cycle of a star.

If scientists only studied stars in visible light, then we would miss much of the picture. The human eye can only see certain wavelengths, within the visible spectrum. Therefore, it is important to use as many dfiffernent tools that we can to observe space. For example, the hot upper layers of the sun emits ultraviolet and X-ray light. Some violent events may even produce gamma rays. So, stars emit light over a broad range of wavelengths. The electromagnetic radiation that is emitted from the surface of the stars is our primary source that we use to study them. The radiation in wavelengths that run from the x-rays to the radio waves can be collected by different kinds of telescopes. Telescopes that study different kinds of wavelengths vary in its structures and designs, but the main idea behind all telescopes is to collect as much light as possible with as much resolution as possible.

Visual (Optical) Telescopes- Optical telescopes collect light from the visual part of the light spectrum. There are three types of optical telescopes: reflectors (uses mirrors), refractors (uses lenses), and catadioptric (uses both, lenses and mirrors).

X-ray Telescopes- observes remote objects in space in the X-ray spectrum. X-ray telescopes are put into space due to the fact that certain wavelengths from stars in space does not penetrate earth's atmosphere (atmosphere absorbs the X-rays). An X-ray telescope on earth would be useless.

Radio Telescopes- observes objects in the radio spectrum. Type of radio telescope used depends on the strength of the signal and the amount of detail that is needed. Observation on the Earth's surface is affected by the wavelengths that passes through the atmosphere. Low frequencies (long wavelengths) is limited by the ionsphere. High frequencies (short wavelengths) is reflected by water vapors (which is why radio telescopes are being built in dry, high spots). Radio telescopes has led to the discoveries of new objects in space such as cosmic microwave background radiation (“Big Bang”), radio galaxies, pulsars, and quasars.

Ultraviolet- some of the hottest, most energetic stars can be seen in ultraviolet light. Can only be used in space as the atmosphere (ozone) absorbs UV light.

Gamma-ray- Gammas are the highest energy and shortest wavelengths. Luckily, our atmosphere absorbs gamma-rays. So a gamma-ray telescope must be used in space. Gamma-ray telescopes have shown us how violent space can be. It has helped us to view things such as black holes, pulsars, and binary stars in a new way.

f. Describe, in terms of color and brightness, how the evolution of a star is determined by a balance between gravitational collapse and nuclear fusion

First of all, stars are born within the coldest and densest clouds. These star-forming clouds are called the molecular clouds because their temperatures allow hydrogen atoms to pair up to form hydrogen molecules. These molecular clouds tend to be quite large, because more total mass helps gravity overcome gas pressure. They typically have temperature of only 10-30 K (typical temperature of earth is 300K). A typical star-forming cloud is thousands of times more massive that a typical star and can give birth to many stars at the same time. Stars are born in clusters.

Once a large molecule cloud begins to collapse, gravity pulls the gas towards the clouds densest regions, causing it to fragment into smaller pieces, where each pieces goes onto form one or more new stars. Each cloud fragment heats up as it contracts (gravitational potential energy) as gravity pulls each part of the cloud fragment closer to the center of the fragment. In the beginning, the contracting gas radiates away much of the heat energy, so the temperature of the cloud remains below 100K (so it glows in long wavelengths infrared light) and prevents temperature and pressure from building enough to resist gravity.

As the cloud continues to collapse, the growing density makes it difficult for radiation to escape. Eventually, the center of the fragment cloud becomes dense enough to trap infrared radiation and temperature and pressure begins to rise dramatically. The rising pressure begins to push back on the gravity, slowing the contraction. The dense center of the cloud fragment in now a protostar. Gas surrounding the protostar continues to “rain down” on it, increasing its mass. The protostar begins to rotate rapidly and rotates faster as it contracts (angular momentum remains conserved). Nuclear fusion is still not taking place, so it's not a true star yet). They can still be quite luminous due to the energy being released by the infalling matter. A disk of gas in produced around the protostar as the protostar rotates. Because angular momentum must be conserved, the gas surrounding the protostar must rotate faster as it contracts. The collision between gas particles tend to flatten this gas into a disk. In our own solar system, the planets formed in the disk region.

Late stages of star formation can be violent. Many young stars send out high-speed streams of gas (jets- shot in opposite directions along the protostars axis (although we still down' know exactly how the jets are generated). The protostars rapid rotation generates a strong magnetic field (which may help channel the jets along the rotation axis and generates a strong protostellar wind which carries away the cocoon of gas surrounding the protostar. This I rune reduces its angular momentum- causing the rotation to slow down. Some stars end up as binary stars when the molecular cloud contracts and break sup into fragments. They made end up close to one another. Gravity can pull them together, and go into an orbit around each other due to the fact that each pair of protstars has a certain mount of angular momentum. A protostar becomes a true star when its internal core reaches temperature of 1- million K (hot enough for nuclear fusion to operate effectively_ The ignition of fusion halts the protostar's gravitational contraction and marks the birth of a star. The energy produced in the core matches the amount of radiated form its surface (internal structure is stabilized).

The length of time from the formation of a protostar to the birth of a main-sequence star depends on its mass. Massive stars do everything faster. There are limits of both the minimum and maximum possible masses of stars. A star must be between .08Msun to 150Msun. Any smaller than this and the protostar will stabilize in size and become a brown dwarf (fuzzy gap between a planet and star). They won't reach the temperatures needed for nuclear fusion and ends up slowly cooing as they radiate away their internal thermal energy. They radiate primarily in infrared and look deep red. They are far dimmer than normal stars. The first brown dwarf was discovered in 1995. The crush of the brown dwarf due to gravity is halted by degeneracy pressure (quantum mechanics) and does not depend on temperature at all. They can only squeeze electrons together so much. Electrons must still have space to move about freely.

a. Explain how the solar system formed, including differences and similarities among the sun, terrestrial planes, and the gas planets, and cite evidence from Earth and moon rocks that indicate its 4.6 billion years ago

The gas that gave rise to our solar system was the product of billions of years of galactic recycling that took place before the birth of our solar system. The gas that made up the solar nebular was made up of approximately 98% hydrogen and helium and 2% everything else. The sun still has this basic composition, while the planets tend to have higher proportions of heavy elements.

In the center of the collapsing solar nebula, gravity drew together enough material to form the sun. IN the disk, the gas was too spread out for gravity to clump it up. Instead, hydrogen clumped in some other way (“seeds”) and grew in size until gravity could star pulling it together into planets.

The small “seeds” that eventually grew into planets was through a process called accretion. The particles didn't really collide together, but more just touched and were held together by electrostatic forces. Eventually, gravity helped it to grw and become a planetesimal.

The particles condensed out of the gas (microscopic) and grew with time. Different materials condense at different temperatures. Hydrogen and helium never condensed under the conditions present in the nebula. Hydrogen compounds (water, methane, ammonia) can solidify at low temperature (below 150K) and under low pressure. Rock condenses between 500K and 1,300K. Metals condenses into solid from 1,000 to 1,600K. Close to the sun, it was far too hot for any materials to condense. Near what is now Mercury's orbit, the temperature was low enough for metals and some types of rocks to condense into solid particles, along the asteroid belt, temperatures were low enough for dark, carbon-rich materials to condense, along with minerals containing small amounts of water. Hydrogen compounds could condense into ice only beyond the frost line. The amount of material was far greater beyond the frost line, so terrestrial planets ended up relatively small in size. Jovian planets formed as gravity drew gas around large, icy planetesimal. With the large amount of ices in the outer solar system large planetesimals grew in mass many times that of the Earth so the gravity became strong enough to capture and hold some of the hydrogen and helium gas that made up the vast majority of the surrounding solar nebula. Eventually, they grew so much that they bore little resemblance to the icy seed that they started with. The same heating, spinning and flattening of disk the solar nebula should have also affected the gas drawn by the gravity of the young jovian planets. Accretion also took place and that's how their moons formed.

Earth's moon may have occurred when a mass the size of a planetesimal smacked into Earth at an angle that sent debris into Earth's orbit. Accretion would have formed the moon. The composition is similar to Earths' outer layers and it contains vaporized ingredients such as water. These gases would not have participated in the process of accretion that formed the moon.

The most reliable method of measuring th age of rocks in through radiometric dating, which relies on careful measurement of the proportions of various atoms and isotopes in a rock. This method works because some atoms undergo changes with time that allows us to determine how long they've been held within the rock's solid structure. Radiometric dating tells us how long it's been since a rock solidified. Moon rocks date back to 4.4 billion years ago. Meteorites are our real source. Meteorites have been dated as far back as 4.53 billion years ago.

b. Know the current evidence for the existence of planets orbiting other stars

The first discovery of a planet around another star, called 51 Pegasi, was in 1995. More than 200 extrasolar planets have since been discovered.

Evidence:

Circumsteller disks- a disk around stars provide the conditions for planet formations

Doppler technique- looks for Doppler shifts in a stars spectrum. As long as a planet's orbit is not face-on to us, then its gravitational influence will cause its star to move alternately slightly toward and way from us. The 1995 discover cam when this star was found to be moving with a rhythmic wobble. This method is best suited to identifying massive planets that orbits relatively close to the star because the stars orbital speed depends on the strength of the gravitation tug and gravity is strongest in massive planets.

Astrometric technique- plants are able to exert gravitational tugs on the sun, each adding a small additional effect to Jupiter's. With this technique, we are able to make precise measurements of a stellar position in the sky. If a star “wobbles” gradually around its average position, we must be observing the influences of unseen planets.

Transits and Eclipses- a way to detect distance planets is to detect slight changes in a star's brightness, which occurs when a planet passes in front of or behind it. When a planet passes between us and the star, the result is a transit. Because other reasons could dim a star's brightness, the dimming needs to repeat with a regular period. When the planet passes behind the star, it is called an eclipse. During an eclipse, we observe/measure the effect of the eclipse from combined light from the star and planet. Whenever either blocks the other, there is a dip that occurs during an eclipse and are usually measurable in infrared wavelengths.

OGLE- Optical Gravitational Lensing Experiment finds using its gravitational lensing, an effect predicted by Einstein's general theory of relativity that occurs when one objects gravity bends or brightness the light of a more distant object. However, the geometry for lensing will never repeat and no opportunity for follow-up observation.

a. Cite various forms of evidence that indicate the proximity of the planets in the solar system in relation to Earth and Stars.

b. Cite various forms of evidence that Earth and other planets change over time

Starting back from the very beginning: According to the Nebular Theory, Earth first formed approximately 4.567 billion years ago when an enormous rotating cloud, which consisted of microscopic dust grains, helium and hydrogen gases, and the ejected matter of dead stars began to rotate and contract. It began to rotate faster and faster (conservation of angular momentum) and eventually, the inward pull of gravity equaled the outward force of the rotation motion of the nebula. The nebula cloud flattened into a disk with most of the matter concentrated in the center, which eventually formed the sun. The gravitational energy was converted to thermal (heat) energy, which caused temperature at the center region of the nebula to rise. On the other hand, the outer region of this nebula remained pretty cold, perhaps around -200 Celsius.

The inner region began to cool and this allowed materials to condense into tiny partials. These tiny particles slowly began to coalesce and accreted into planetesimal, which eventually formed the four inner planets. The inner planets are made up of minerals such as silicon, calcium, sodium. The planetesimal and materials that did not form into planets collided into the planets. These bombardments caused the planets to a rise in temperature. Thus, because of the high temperatures and weak gravitational fields, they were unable to hold on to the lighter components of the nebular cloud, such as hydrogen and helium. These elements, which made up the first atmosphere, were eventually blown away by solar radiation. On Earth outgassing (volatiles escaping to the surface of the earth) is thought to have formed a second atmosphere. Most of the gases that made up of the second atmosphere was water vapor, small amounts of hydrogen, hydrogen chloride, carbon dioxide, carbon monoxide, nitrogen, and other gases. The atmosphere was originally anoxic (based on the amount of BIF's formed during this time period). Life began to form consisted of simple one-celled prokaryotic organisms that formed during the archan era. Around 3.5 bya, photosynthetic prokaryotes (mainly cyanobacteria) began releasing oxygen into the ocean, which eventually made its way to the atmosphere. Proof of oxygen levels rising during the Proterozoic Eon are the formation of redbeds, which are sediments that contain oxidized iron-bearing minerals.

For the inner planets, with the bombardments and radioactive decay, the internal temperature of the planets rose. The planets became hot enough for iron and nickel to melt. These heavy, high-dense, melted metals began to sink towards the center of the planet. The less buoyant masses (which consisted of elements such as oxygen, silicon, and aluminum) of molten rock rose toward the surface of the planet where they eventually solidified to form a primitive crust. The planets started to divide chemically into layers: the inner solid iron-rich core, the liquid out core, the viscous mantle, and the crust.

The atmosphere of the Earth and on some other planets such as Venus and Mars has also gone through changes over time. I explained the changes of Earth's atmosphere here, in part B. And I described some of the atmospheric changes that occurred on Venus and Mars, in the Earth's Energy Budge-Inflow and Outflow in part D Section.

The Earth has gone through some major tectonic changes. I described many of the tectonic changes in the Planet Earth category, section A, titled Tectonic Processes.

One of the biggest changes that will greatly affect the planets in the solar system will occur when the sun begins to die. Our sun's lifespan as a main-sequence star is only about 10 billion years or so, before it begins to undergo drastic changes. Our sun is a mediocre star, on the main-sequence. Once our sun has fused up all of it's hydrogen into helium, then fusion will cease. There won't be anymore supply to the thermal energy and it won't be able to maintain the thermal pressure anymore. Without the pressure, the sun won't be able to push against gravity and the sun will begin to shrink in on itself. The sun will now enter into a new stage. The sun's outer layers will begin to expand outward as the core continues to shrink as gravity pulls it in. In a span of about 1 billion years, the sun will continue to grow in size and will become a red giant. The sun will become more than 100 times larger than it is today. The reason why the sun's outer layers expand while the core shrinks lies at the core. When the core has used up all of the hydrogen, then only helium will be left. In the surrounding layers of the sun, however, there are still hydrogen atoms that are able to still continue to undergo fusion. A hydrogen shell burning takes place outside of the core. In this region, it becomes hot enough for the fusion of hydrogen in the shell to take place. This region becomes so much hotter than the core and a much higher fusion rate will take place. This will result in the sun's luminosity to increase and to have enough pressure to push the outer layers outward, pushing the sun into the red giant category. This growth will cause gravity to become a bit weak and much of the sun's mass will escape in a stellar wind. This event will continue as long as the helium in the core continues to remain inert. The core continues to shrink as gravity pulls it in further and it begins to grow hotter and denser. As a result, the fusion in the shell continues to increase, which produces even more helium for the core. This cycle continues. The core continues to grow hotter and denser as the hydrogens in the shell continue to fuse and feeds more helium to the core, and as the core grows hotter, fusion in the shell increases. As the core continues to shrink, the sun's outer layers will continue to expand and grow larger and more luminous. This will continue until the temperature in the core reaches of around 100 million K. Then, it will be hot enough for the helium nuclei to begin fussing together. Now, the sun has entered a new stage. At this point, the next step will depend on the mass of the star. Typically, low-mass starts, like our sun will enter the helium burning stage. Other low-mass stars may be so low that their core may never become hot enough to fuse helium. For these stars, the core eventually collapses and becomes a helium white dwarf.

So, when the sun enters the helium burning stage, the helium fusion requires much more energy in order to ram into each other than hydrogen. 3 helium nuclei fuse to form one carbon nucleus plus energy. The rising temperature in the core causing helium fusion rate to increase drastically called a helium flash. This helium flash releases a great amount of energy into the core. This causes thermal pressure to overcome degeneracy pressure and is able to push out on the core, causing it to expand. This expansion pushes the shell outward and causes it to decrease in temperatures, which reduces fusion rate. So, even though helium and hydrogen fusion are taking place, the total amount of energy production to fall. This results in a drop in the sun's luminosity and size as the outer layers contract.

Then, after about 100 million years, the helium in the sun's core will have fused all into carbon. The core, once again, will shrink from the pull of gravity. The sun will expand again, as a red giant. The only difference now is the shell will be of helium fusion around the inert carbon core, with the hydrogen shell on top of the helium shell. It is now a double-shell burning star. These double shells will contract against the core, which will increase their temperature and fusion rate extremely high and will cause the sun to expand to an even greater size and luminosity than ever before. The fusion in the hydrogen shell will last for a few million years or so. In a low-mass star, such as the sun,fusion of the carbon in the core will not take place as it won't reach temperature needed for fusion to take place. The degeneracy pressure will stop the collapse of the sun's carbon core, before it gets hot enough. At this point, the sun's life has come to an end.

The luminosity and radius and wind keeps growing, while temperature begins to drop. The interstellar dust grains begin to form as a result of the heavier elements condensing into microscopic solid particles of dust. These are blown into interstellar space from steller wind. The sun's death will be beautiful. As the outer layers are ejected into space, it will expose the huge shell of gas that is expanding away from the carbon core. The exposed core will be very hot and will emit ultraviolet radiation, which will ionize the gas in the shell. This will result in a bright glow as a planetary nebula (which has nothing to do with planets). This glow will begin to fade as the core begins to cool. The gas will have all been ejected into space. The carbon core will become a white dwarf. White dwarf's are small in radius but very dense. This white dwarf will continue to cool and eventually won't emit any more visible light.

The death of our sun will have big effects on the planets in the solar system. Even way before the sun starts to go through it's dying stages, within the next 5 billion years, there will be slight changes in the sun that will affect Earth. Within the next 5 billion years, the sun will slowly start to become more luminous. This will cause a runaway greenhouse effect on earth and is thought to start anytime within 1 to 4 billion years from now. This runaways greenhouse effect will cause the oceans on earth to boil away. Temperatures will increase dramatically around the time the sun fused all of the hydrogen. Conditions on earth will just become even more worse when the sun becomes a red giant. The temperature of earth will reach around 1,000 K. It is thought that Saturn's moon, Titan, will reach temperatures similar to what Earth has now (from well below freezing). So, perhaps any humans who MAY still be alive at this point may want to high-tail it out to Titan. As the sun begins to shrink and cool after the helium flash turns the sun into a helium-burning star, then it will provide a temporary break on Earth from these extreme hot conditions. Once the sun has exhausted all of the helium in its core, then the sun will once again expand even greater than the red giant phase and will grow out all the way to Earth's orbit. When the sun ejects its outer layers, it will engulf Jupiter and Saturn. Of course, this scenario will occur if the planets continue its orbit around the sun. Once the sun has become a white dwarf, by then, there won't obviously be any more gravitational pull and any remaining planets, comics, etc, will fly off into space. c. Describe the influence of collisional process on early earth and other planetary bodies in terms of shaping planetary surfaces and affecting life on Earth.

The collision, heavy bombardments in the first few hundred million years did more than just batter the planets. They also brought materials from other regions of the solar system, a fact that is critical to our existence on Earth today. These impacts are left over planetesimal. Planetesimals that grew within the inner solar system were made from metal and rock. Thus, the planetesimals probably contained no water or Hydrogen compounds since it was too hot for these compounds to condense in our region of the soar nebula. Thus, water and other hydrogen compounds were brought to Earth through impacts of water-bearing planetesimals that formed farther from the sun.

Our moon may also have formed when a Mars-size planetesimal hit the Earth at such an angle that broke off parts of the Earths outer crust. Eventually, moon acclimated and grew.

Pluto's moon, Charon, shows signs of having formed in a giant impact, similar to our moon.

Mercury's high density may be the result of a giant impact that blasted away its outer, lower density layers.

Impacts could have also been responsible for tilting the axis of may planets (including Earth's) and tipping Uranus on its side.

Venus' slow and backward rotation could also be the result of a giant impact.